First, a frame structure of a wireless communication system will hereinafter be described with reference to FIG. 1. FIG. 1 is a diagram illustrating a frame structure of Long Term Evolution (LTE) system. Referring to FIG. 1, one frame includes 10 subframes, and one subframe includes two slots. A time required for transmitting one subframe is defined as a Transmission Time Interval (TTI). For example, one subframe may have a length of 1 ms, and one slot may have a length of 0.5 ms.
One slot may include a plurality of Orthogonal Frequency Division Multiplexing (OFDM) symbols. The OFDM symbol may be called an SC-FDMA symbol or a symbol duration.
One slot may include 7 or 6 OFDM symbols according to a cyclic prefix (CP) length. The LTE system includes a normal CP and an extended CP. In case of the normal CP, one slot may include 7 OFDM symbols. In case of the extended CP, one slot may include 6 OFDM symbols.
In order to transmit resource allocation information of each subframe at intervals of a subframe, an eNode B (eNB) transmits a physical downlink control channel (PDCCH) to 0th to 2nd OFDM symbols (in case that a starting one from among the OFDM symbols of a subsframe is the 0th OFDM symbol). In this case, according to the amount of PDCCH, PDCCH can be transmitted to the 0th OFDM symbol, the 0th to 1st OFDM symbols, the or 0th to 2nd OFDM symbols.
FIG. 2 shows a resource structure of one DL slot. Referring to FIG. 2, one slot includes 7 OFDM symbols. A resource element (RE) is a resource region including one OFDM symbol and one subcarrier. A resource block (RB) is a resource region including a plurality of OFDM symbols and a plurality of subcarriers. For example, the RB may include 7 OFDM symbols in a time domain and include 12 subcarriers in a frequency domain. The number of RBs contained in one slot may be determined according to a DL bandwidth.
In a general wireless communication system, direct signal communication is achieved between a fixed eNB and a UE through a link, such that a high reliability wireless communication link can be easily configured between the eNB and the UE. However, since the wireless communication system may have a fixed eNB, it has low flexibility in wireless network configuration. In addition, the conventional wireless communication system has difficulty in providing an efficient communication service to a wireless environment that experiences either poor traffic distribution or serious variation in numbers of call-connection requests. In order to obviate the above-mentioned disadvantages, a data transmission scheme of a fixed relay node, a data transmission scheme of a mobile relay node, or a relaying-node data transmission scheme of general UEs can be applied to a wireless communication system.
FIG. 3 is a diagram illustrating a wireless communication network using a relay node (RN).
The relaying wireless communication system may reconfigure a network by rapidly responding to communication environment variation, and may more efficiently operate the entire wireless network. For example, the relaying wireless communication system increases a cell service region and system capacity. That is, if a channel condition between the eNB and the UE is poor, a relay node (RN) is installed between the eNB and the UE and a relaying path is configured through the relay node (RN), such that a radio frequency (RF) channel having superior channel conditions can be provided to the UE.
In addition, a relay node (RN) is introduced to a cell edge region having a poor channel condition such that it can provide a higher-speed data channel and can extend a cell service region.
As described above, the relay node (RN) has been widely used to solve the propagation shade region in a mobile communication system. Compared to the conventional art that is restricted to functions of a repeater capable of amplifying/transmitting a signal, the latest technology is being developed to cover more intelligent techniques.
Furthermore, the relay node (RN) technology can reduce costs associated with increasing the number of eNBs and maintenance costs of a backhaul network in next generation mobile communication systems, and is requisite for extending the service coverage simultaneously while increasing the data processing rate. With the increasing development of relay node (RN) technology, the necessity for the relay node (RN) used in the conventional wireless communication system to be supported by the new wireless communication system is also increasing.
In FIG. 3, a link between the eNB and the RN is defined as a backhaul link. If transmission of data using DL frequency band or DL subframe resources is achieved in a backhaul link, this backhaul link is referred to as backhaul downlink. If transmission of data using UL frequency band or UL subframe resources is achieved in a backhaul link, this backhaul link is referred to as backhaul uplink. In addition, the connection link between the RN and the UE is defined as an access link. If data transmission is achieved in an access link using a DL frequency band or DL subframe resources, this access link is referred to as access downlink. If data transmission is not achieved in an access link using a UL frequency band or UL subframe resources, this access link is referred to as access uplink.
A plurality of relay nodes (RNs) may exist in one eNB, and the eNB may have to transmit common control information of the RNs.